The present disclosure relates in general to patient monitoring systems including a patient monitor, one or more optical sensors, and a communication cable or device transferring signals between the monitor and the sensor(s).
Standard of care in caregiver environments includes patient monitoring through spectroscopic analysis using, for example, oximeter technologies commercially available from Masimo Corporation of Irvine. Devices capable of spectroscopic analysis generally include light sources transmitting optical radiation into a measurement site, such as, body tissue carrying pulsing blood. After attenuation (e.g. via transmission through tissue, reflectance, etc.) by tissue and fluids of the measurement site, one or more photodetection devices detects the attenuated light and outputs one or more detector signals responsive to the detected attenuated light. One or more signal processing devices process the detector(s) signal(s) and output a measurement indicative of a blood constituent of interest, such as, glucose, oxygen, methemoglobin, total hemoglobin, other physiological parameters, or other data or combinations of data useful in determining a state or trend of wellness of a patient. Such combinations often include statistical analysis of one or more measurements or combinations of different parameter measurements into useful information.
In addition to the foregoing, considerable efforts have been made to develop noninvasive oximeter techniques for measuring other blood analytes or patient parameters, including for example, glucose, total hemoglobin, or the like. Unfortunately, some of these parameters have proven to be difficult to measure using noninvasive spectroscopy. For example, the biologic tissue and water of a measurement site have a high intrinsic absorption at many of the wavelengths of light that are useful in measuring blood glucose. Moreover, blood glucose exists in relatively low concentrations comparatively with other blood analytes. Furthermore, different patients will have large variations in the optical properties of their skin and blood composition.
Moreover, ambient and/or environment interference (i.e., noise) can adversely affect the measurement accuracy. Interference is generated by many commonly-used electrical devices. In a typical household for example, electric power lines and outlets, ambient lights, light dimmers, television or computer displays, and power supplies or transformers generate electromagnetic interference. For example, noise caused by ambient light will generally vary with a periodicity corresponding to a 50 Hz or 60 Hz fundamental frequency and its harmonics. As will be understood by those of skill in the art, the ambient light frequency is a function of the frequency of electricity powering the ambient lights and other interfering devices and/or the frequency of naturally occurring light. The ambient light frequency will, accordingly, change depending on the power system used to operate the devices creating the ambient light. Harmonics of the fundamental ambient light frequency are important because the ambient light can still cause significant interference at the harmonic frequencies. This is particularly true when the ambient light is provided by fluorescent lights which generate significant noise at the second harmonic (i.e., 100 Hz or 120 Hz) and the fourth harmonic (i.e., 200 Hz or 240 Hz). In addition in typical care environments medical equipment (e.g., electrocauterization devices) also generates significant electromagnetic interference. These and other challenges make signal information indicative of physiological parameters (e.g., glucose) difficult to differentiate from the interference signal. Moreover, patients and other users often desire glucose and other physiological parameter data in at least spot check measurements in a wide variety of care and non-care environments where interference levels are unknown.